The use of heavy duty trailers and semi-trailers for transportation of heavy and/or bulky loads is very well known in the industry, and various types of such trailers and semi-trailers (referred to herein as "trailers" for convenience) have been developed in response to specific needs and problems related to various types of loads. Particularly, trailers designed to provide a load carrying platform or bed disposed low to the ground in order to achieve a lowered center of mass have been and continue to be widely used for the transportation of heavy construction or industrial equipment, which is typically characterized by a combination of bulky size, heavy weight, and relatively high center of mass. The design most commonly used to provide a lowered load platform is known as a gooseneck design, in which the nose of the trailer is at the height of the tow tractor or truck coupling mechanism and is interconnected to the lowered load platform through a vertical or slanted member.
Because of the size and weight of the equipment which is typically transported on such trailers, it is often impractical or impossible to hoist the equipment onto the trailer, and, because such equipment is often loaded and unloaded in the field, it is often equally impractical or impossible to utilize a loading dock or suitable loading ramp to drive the equipment onto the trailer. As a result, various means of lowering the nose, or coupling end, of the trailer to or near the ground, to allow equipment to be driven or winched onto the trailer, have been devised.
The most common approach known in the prior art is a heavy duty "gooseneck" type trailer provided with a folding neck, as illustrated by U.S. Pat. No. 3,756,443 to Verschage, et.al., U.S. Pat. No. 3,883,019 to Hansen, Jr., and U.S. Pat. No. 3,894,645 to verschage. Trailers made in accordance with this approach suffer from the disadvantage of limited useable load space on the bed of the trailer, as a result of the inability to carry any load over or on the neck portion of those trailers. Those trailers have the additional disadvantages of relatively high cost and maintenance requirements, arising from the mechanical complexity of the folding neck arrangements.
Another approach to facilitate the loading of equipment onto a trailer involves lowering of one end of the trailer to the ground, wherein the trailer pivots on its road wheels. One example of this general approach is found in French Patent No. 2,371,315 to Gatserelia, in which a multi-stage telescoping prop is disposed near the front or nose of the trailer for the purpose of providing a direct lifting force to raise and lower the nose of the trailer. Another example is found in British Patent No. 2,107,274 to Jones, which discloses a pivoting support leg disposed near the nose of the trailer and actuated by a hydraulic or pneumatic arm. During operation of the pivoting support leg designs of the prior art the trailer does not move longitudinally relative to the ground, and the ground contact end of each support leg is forced to move along the ground as the nose of the trailer is raised or lowered. To facilitate such movement, the ground contact end of each support leg is typically provided with one or more small wheels which are intended to roll along the ground surface.
While the general approach of providing a non-articulated trailer with one end adapted to be dropped to the ground offers advantages over the folding gooseneck approach, the specific designs of the prior art are prone to their own set of disadvantages. Both the direct lift approach and the pivoting support leg approach of the prior art have been associated with a relatively high load platform height to provide sufficient ground clearance for operation of their lifting mechanisms. The need for the ground contact end of each support leg of the pivoting support designs to move along the ground often presents problems, especially when used on a relatively soft unpaved surface, as the end of each support leg displays a pronounced tendency to dig itself into the ground rather than rolling over it. With heavy trailer loads, this problem may become rather severe, even on paved surfaces. Further partially as a result of problems with movement of the ground contact end of each support leg over the ground, the pivoting support leg designs known in the prior art suffer significantly from leverage disadvantage, and the load carrying capacity of the trailer itself may well exceed the effective working capacity of the lift actuating mechanism.
Accordingly, there has remained a need in the industry for a power actuated drop-nose trailer which allows the complete platform of the trailer to be utilized, which provides a low center of mass, and which provides a lifting mechanism capacity closely compatible with the load carrying capacity of the trailer itself.